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# m6l15 - Module 6 Shear Bond Anchorage Development Length...

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Module 6 Shear, Bond, Anchorage, Development Length and Torsion Version 2 CE IIT, Kharagpur

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Lesson 15 Bond, Anchorage, Development Length and Splicing Version 2 CE IIT, Kharagpur
Instruction Objectives: At the end of this lesson, the student should be able to: understand the importance of bond and why is it essential to provide between steel and concrete, explain the development length, understand the need for anchoring the tensile bars, justify the superiority of deformed bars to smooth mild steel bars, define the design bond stress, understand the reason for different values of design bond stresses of plain bars and deformed bars in tension and compression, determine the development length of a single bar and bars bundled in contact, derive the expression to check the development length of bars in tension, specify the salient points of anchoring bars in tension, compression and shear, determine the bearing stress and check the same, take adequate precautions when the direction of reinforcement changes, specify the salient points of splicing and welding of reinforcement to make it longer, apply the theory for designing beams in different situations as may arise. 6.15.1 Introduction The bond between steel and concrete is very important and essential so that they can act together without any slip in a loaded structure. With the perfect bond between them, the plane section of a beam remains plane even after bending. The length of a member required to develop the full bond is called the anchorage length. The bond is measured by bond stress. The local bond stress varies along a member with the variation of bending moment. The average value Version 2 CE IIT, Kharagpur

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throughout its anchorage length is designated as the average bond stress. In our calculation, the average bond stress will be used. Thus, a tensile member has to be anchored properly by providing additional length on either side of the point of maximum tension, which is known as ‘Development length in tension’. Similarly, for compression members also, we have ‘Development length L d in compression’. It is worth mentioning that the deformed bars are known to be superior to the smooth mild steel bars due to the presence of ribs. In such a case, it is needed to check for the sufficient development length L d only rather than checking both for the local bond stress and development length as required for the smooth mild steel bars. Accordingly, IS 456, cl. 26.2 stipulates the requirements of proper anchorage of reinforcement in terms of development length L d only employing design bond stress τ bd . 6.15.2 Design Bond Stress τ bd (a) Definition The design bond stress τ bd is defined as the shear force per unit nominal surface area of reinforcing bar. The stress is acting on the interface between bars and surrounding concrete and along the direction parallel to the bars.
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